1. Field of the Invention
The present invention relates to an iron-based amorphous alloy thin strip suitable for use as a wound transformer material, and more particularly, to an iron-based amorphous alloy thin strip which assures an improved ratio (building factor) of the iron loss of a wound core obtained by using the iron-based amorphous alloy thin strip to the iron loss of a single unwound strip.
2. Description of the Related Art
A so-called amorphous alloy thin strip having a thickness of several tens of .mu.m and a disordered atomic array is obtained by ejecting, for example, a Fe--B--Si type molten alloy onto the surface of a cooling roll rotating at high speed by the single roll process or the like and thereby rapidly solidifying the molten alloy at a cooling rate of 10.sup.5 to 10.sub.6 .degree. C./s. Such an amorphous alloy thin strip is disclosed in Japanese Patent Laid-Open Nos. Sho 54-148122, Sho 55-94460 and Sho 57-137451.
Such an amorphous alloy thin strip is readily magnetized and exhibits magnetic characteristics including iron loss. Thus, it has been put to practical use as an iron core material for transformers.
However, although such a Fe--B--Si three-element type amorphous alloy thin strip assures a relatively low iron loss, improvement in the iron loss is quite limited. Hence, attempts have been made to add various elements to the above-described three-element type amorphous alloy as fourth components.
For example, Japanese Patent Publication No. Hei 1-54422 proposes a Fe--B--Si type amorphous alloy in which Mn and Ni are present in an amount of 0.5 to 3 at % as an iron-based amorphous alloy having a low iron loss and exhibiting excellent insulation coating properties.
Japanese Patent Laid-Open No. Sho 62-192560 proposes a Fe--B--Si type amorphous alloy in which at least one element selected from Cr, Mo, Ta, Mn, Ni, Co, V, Nb and W is present in an amount of 0.05 to 5 at % and which has a surface roughness adjusted by, for example, rolling.
Neither Japanese Patent Publication No. Hei 1-54422 nor Japanese patent Laid-Open No. Sho 62-192560 gives consideration to the magnetic characteristics of a wound core obtained from the amorphous alloy, although Japanese Patent Publication No. Hei 1-54422 refers to an improvement in the interlayer insulation in a laminated structure and Japanese Patent Laid-Open No. Sho 62-192560 refers to an improvement in the space factor of a laminated structure.
Japanese Patent Laid-Open No. Hei 5-132744 discloses an alloy in which Sn is added to the Fe--B--Si type alloy to increase the saturation magnetic flux density without deteriorating iron loss and magnetic permeability, and a method of manufacturing an iron core using such an alloy.
The example of the iron loss (W.sub.13/50) given in Japanese Patent Laid-Open No. Hei 5-132744 is 0.2 W/kg or above in a toroidal wound core. This value, however, is not low enough to meet the requirements made in recent years.